Linear indexers, also known as linear stepper motors, have heretofore been proposed in the art for obtaining precisely incrementally controlled linear motion at an output shaft or the like. In particular, electromagnetic actuators of the described character have comprised a shaft carrying a series of magnets and cooperating with a series of stator assemblies for electromagnetically incrementing or indexing the magnets and shaft through the stator assemblies. Linear indexers of this type are expensive to fabricate and assemble. Moreover, the length of stroke is necessarily limited by the number of magnets and stator assemblies, with cost and size increasing rapidly with stroke length. Holding power, which is a function of electromagnetic attraction between the magnets and energized stator assemblies, has severely limited application of this technology.
It is a general object of the present invention to provide a linear actuator, particularly an actuator for obtaining incrementally indexed linear motion, which is inexpensive to manufacture and implement, which can be readily and accurately controlled over an unlimited length of stroke, and which obtains high holding power with limited energy input. A further and more specific object of the invention is provide an electromagnetic linerally indexing actuator of reduced cost and size, and suitable for use in precision control of electronic functions in an automotive vehicle, such as precision control of the pintle in an EGR valve of a vehicle emission system, or in power-assisted electronic vehicle applications such as power steering or braking.